1. Field of the Invention
The present invention relates to a copolycarbonate. More particularly, the present invention is concerned with a novel copolycarbonate comprising 1,6-hexanediol and 1,5-pentanediol units in specific molar ratios. The present invention is also concerned with the use of the above-mentioned copolycarbonate as a novel structural component for polymers, such as a polyurethane and thermoplastic elastomers. The copolycarbonate of the present invention and polymers derived therefrom have excellent resistance to hydrolysis, light, chlorine, oxidative degradation, heat, etc.
2. Discussion of Related Art
A polyurethane and a urethane-, ester- or amide-based thermoplastic elastomer are widely used in the art. The soft segments of the polyurethane and thermoplastic elastomer are generally composed of structural units derived from a polyester polyol and/or a polyether polyol both having a hydroxyl group at each of the molecular terminals thereof. In this connection, reference is made to U.S. Pat. Nos. 4,362,825, 4,374,935 and 4,129,715.
A polyester polyol, such as a polyadipate polyol, is poor in hydrolysis resistance. Accordingly, for example, a polyurethane comprising, as soft segments, structural units derived from a polyester polyol has a disadvantage in that cracks are likely to occur and mold is likely to grow on the surface of the polyurethane within a relatively short period of time.
On the other hand, a polyurethane comprising structural units derived from a polyether polyol has desirable hydrolysis resistance. However, the polyurethane has a disadvantage in that it is poor in resistance to light, oxidative degradation and chlorine.
The above-mentioned disadvantages of the polyurethane are attributed to the presence of ester groups and to the presence of ether groups, respectively, in the polymer chain.
As in the field of a polyurethane, improvement of a polyester- or polyamide-based thermoplastic elastomer in resistance to heat, light, hydrolysis, mildewing and oil has recently been strongly desired in the art.
On the other hand, a sealant comprising an aliphatic polyether or polyestherester having a methyldiacetoxysilyl group at each of the molecular terminals thereof is known in the art, as disclosed, for example, in Japanese Patent Application Laid Open Specification No. 50-15699. Such a sealant has, however, a disadvantage in that it is poor in resistance to light, oxidative degradation and chlorine due to the presence of ether groups in the polymer used as the component for the sealant.
A polycarbonate polyol prepared from 1,6-hexanediol is being marketed as a material for providing soft segments which have desirable resistance to hydrolysis, light, oxidative degradation, heat and chlorine. This resistance is believed to be due to the fact that the carbonate bond of the polymer chain has excellent chemical stability.
However, a polyurethane and a polyester-based elastomer, each comprising structural units derived from a polycarbonate polyol having 1,6-hexanediol residues, disadvantageously exhibit extremely poor flexibility and elastic recovery, as compared to those of a polymer comprising structural units derived from other polyols, such as a polyether polyol. Further, as shown in Comparative Example 13, it is difficult to produce a fiber from the polyurethane because of the poor spinnability of the polymer.
To alleviate these problems, various proposals have been made. For example, it was proposed in U.S. Pat. No. 3,639,354 and European Pat. No. 135848 to use, as a polyol component, a polycarbonate prepared from a mixture of 1,6-hexanediol and a diol having an ether group, which is effective for lowering to some extent the softening temperature of the final polyurethane. Such introduction of ether groups is useful for providing a polyurethane which has improved flexibility, but such a polyurethane is disadvantageously poor in resistance to light, chlorine and oxidative degradation.
In U.S. Pat. No. 4,103,070 and U.S. Pat. No. 4,101,529, it was proposed to use, as a polyol component, a polycarbonate diol synthesized from a mixture of 1,6-hexanediol and 1,4-cyclohexanedimethanol. In the patents, it is disclosed that the use of the polycarbonate diol will yield an amorphous polyurethane. While the crystallinity of the final polyurethane can be lowered, the cyclic ring introduced into the polyurethane imparts increased hardness to the polyurethane. Consequently, with respect to the polyurethane, flexibility improvement is not satisfactory.
In Japanese Pat. Application Laid-Open Specification No. 60-195117, it was proposed to use, as a polyol component, a polycarbonate diol synthesized from a mixture of 3-methyl-1,5-pentanediol, 1,6-hexanediol and 1,9-nonanediol. In the Laid-Open specification, it is disclosed that the final polymer exhibits improved flexibility. While the crystallinity of the polymer is lowered by the incorporation of side chains, the side chains also cause the polymer to exhibit poor resistance to light and oxidative degradation. In the Laid-Open specification, the use of 3-methyl-1,5-pentanediol is limited to at most 50% by weight when high resistance is required to heat, light and oxidative degradation.
In U.S. Pat. No. 4,013,702 and U.S. Pat. No. 4,105,641, the synthesis of a copolycarbonate from a mixture of 1,6-hexanediol and 1,4-butanediol is described. These patents relate to a method for synthesizing a copolycarbonate. In the patents, there is no description relating to the properties of the copolycarbonate. But, according to tests (as shown in Comparative Example 14), the elastic recovery of the final polymer is not sufficient, and when production of polyurethane fiber is desired, spinning is difficult to due to the poor spinnability of the polymer. Moreover, it is noted that (as shown in Comparative Example 11) the elastic recovery is not sufficient with respect to a copolycarbonate synthesized from a mixture of 1,6-hexanediol and 1,9-nonanediol.
As apparent from the foregoing, all of the copolycarbonates known in the art have some inherent problems, which limit their applications.